True... however, I do want to note that coming from Futaba, the receivers (the ones I know to be available anyway) are considerably larger than the other big brands. It usually took some creativity (and a Dremel in the chassis) to make everything fit. To give you an idea of the difference:
Futaba R603FS
I have seen flatter receivers from Futaba, but not with a much smaller footprint. The FF210 buggy was built to accomodate large electronics (from personal experience I know the hassle of small electronics bays), and even here you can see it's not a breeze. Usually I had to mount it on its side to make it work.
KO Propo KR-413FH
Note that the KO receiver you see here is the top-end unit: The more affordable units have a slightly larger footprint but are still more compact. The EX-1 comes with this top-end receiver, the EX-2 comes with the more affordable KR-241FH receiver but is compatible with the top-end receiver as well. Also a nice detail are the plugs that you can use to seal off the receiver slots you don't use: It keeps dirt and dust from getting in your RX that can cause interference issues over time (when it accumulates).